1. Field of the Invention
The present invention relates to an internal combustion engine controller for driving a load by using a high voltage obtained by boosting a battery voltage, in an automobile, a motorcycle, a farm machine, a machine tool, a marine engine and the like which use gasoline, light oil and the like as a fuel, and particularly relates to an internal combustion engine controller preferable in driving a cylinder injection direct injector.
2. Background Art
Conventionally in the internal combustion engine controllers of an automobile, a motorcycle, a farm machine, a machine tool, a marine engine and the like which use gasoline, light oil and the like as fuels, those including injectors which directly inject a fuel into cylinders have been used for the purpose of enhancement of fuel efficiency and output power, and such an injector is called “a cylinder injection direct injector” or “direct injector” or simply called “DI”. As compared with the method which makes a gaseous mixture of air and a fuel and injects the mixture into a cylinder, and is a main stream of the present gasoline engines, the engine using a cylinder injection direct injector requires high energy for a valve opening operation of the injector, since the engine uses the fuel which is pressurized at a high pressure. Further, in order to enhance controllability in high-speed revolution, the high energy needs to be supplied to the injector in a short time.
Many of the conventional internal combustion engine controllers which control the cylinder injection direct injectors adopt the method which provides a boost circuit which boosts a voltage to a voltage higher than the battery voltage, and increases the current which is passed to the injectors in a short time by using the generated boost voltage. The peak current of a typical direct injector is about 5 times to 20 times as large as the injector current of the method which prepares a gaseous mixture of a fuel and air and injects the mixture into the cylinder, and is a main stream of the present gasoline engines.
Quick valve closure of an injector after injecting a fuel into a cylinder is effective in reducing difference in response time due to variations among the injectors of the respective cylinders, and by extension, reduction of the variations in the fuel injection amount among the cylinders, in making the control of the fuel injection amount more accurate, and in reducing useless injection of the fuel to improve fuel efficiency since the valve closing response speed becomes high, and therefore, it is necessary to shorten the drop time of the injector current and cut of the current quickly.
However, in an injector, high energy is accumulated since the injector current flows therein, and in order to cut off the current, the energy needs to be eliminated from the injector. In order to realize this within a short time, various methods are adopted, such as the method which converts energy into thermal energy by using the Zener diode effect of the downstream side switch element (FET) of the drive circuit which drives an injector current, and the method which causes the boost capacitor of the boost circuit to regenerates the injector current through a current regenerating diode. In any method, in order to speed up drop of the injector current, the energy elimination amount per hour from the injector needs to be increased.
In the former method, energy elimination is performed by converting the energization energy of the injector into thermal energy with the downstream side switch element (the third switch element for sink) by using the Zener diode effect as described in JP Patent Application Publication No. 2003-106200 A. In order to increase the energy elimination amount per hour from the injector, it is necessary to select the components with a high Zener diode voltage, but if the Zener diode voltage becomes high, the thermal energy which is generated in the downstream side switch element becomes large, and therefore, the method is not suitable for the drive circuit which uses a large current.
In contrast with this, in the latter method, the electric energy of the injector is regenerated by the boost circuit through the current regenerating diode which is connected to the boost circuit from the downstream side of the injector, and therefore, even if a large current is passed to the injector, heat generation of the drive circuit can be suppressed to be relatively low. However, since the voltage of the regeneration destination is fixed to the boost voltage (100A), the elimination amount per hour of the electric energy of the injector and the drop time of the injector current substantially depend on the boost voltage, and are limited.
From above, in order to cause the boost circuit to regenerate the electric energy of the injector, and drop the injector current quickly while generation of the thermal energy of the drive circuit is suppressed as much as possible, enhancement of the voltage of the regeneration destination of the injector current is desired.